Coordinated changes in photosynthetic machinery performance and water relations of the xerophytic shrub Ziziphus lotus (L.) Lam. (Rhamnaceae) following soil drying

Aim of this study was to investigate the effect of water shortage in wild jujube plants, Ziziphus lotus (L.) Lam, and how it is related to its ecological success. All leaf anatomical traits were significantly affected following soil drying. Stressed plants displayed more negative stem water potential (psi(w)) and osmotic potential values of ca. -3.5 and -4.5 MPa, respectively, after 30 d. The relative water content declined although it still maintained high values (>= 75%). The net photosynthetic rate, stomatal conductance, and transpiration rate were significantly inhibited as psi(w) decreased. However, the intrinsic water-use efficiency increased as water deficit was intensified; the difference became significant only after 30 d. As a consequence, the effective quantum yield of PSII photochemistry and the photochemical quenching coefficient significantly decreased although the maximal quantum yield of PSII photochemistry ratio remained statisticaly unchanged. Plants could maintain their water status sufficiently by increasing proline 1.7-fold and sucrose 1.8-fold in their leaves, respectively. The largest accumulation of both solutes may avoid photodamages at cellular level and play a critical role in maintaining osmotic adjustment.